FIG. 12 is a cross-sectional view showing a conventional wavelength converting device which is disclosed in, for example, JP 11-271820 A. In FIG. 12, reference numeral 1 denotes a vacuum vessel; 2 denotes a non-linear optical crystal such as cesium/lithium/borate (chemical expression: CsLiB6O10 (CLBO)); 3a and 3b denote optical windows; 4a, 4b and 4c denote O-rings; 5 denotes a vacuum sealing valve; and 6 denotes a fixing fitting. Reference numeral 7 denotes an entire wavelength converting device.
Subsequently, the operation will be described. A laser beam enters the inside of the vacuum vessel 1 from the optical window 3a at an input side, and interacts with the non-linear optical crystal 2 so as to be subjected to wavelength conversion. Thereafter, the laser beam is outputted from the optical window 3b at an output side. A top portion of the vacuum vessel 1 is disposed with the vacuum sealing valve 5, and the boundaries between the main body of the vacuum vessel 1 and the optical windows 3a, 3b and vacuum sealing valve 5 are sealed with the O-rings 4a, 4b and 4c, and the interior of the vacuum vessel 1 is maintained in vacuum.
In the interior of the vacuum vessel 1, the non-linear optical crystal 2 is pushed by the fixing fitting 6 from the upper so as to be fixed onto a bottom portion of the vacuum vessel 1.
As described above, since the conventional wavelength converting device maintains the atmosphere around the wavelength conversion crystal in vacuum, impurities are liable to occur from the vacuum vessel, the O-rings, the fixing fitting and so on which are exposed to vacuum, and the impurities are stuck onto the non-linear optical crystal 2 (wavelength conversion crystal) and the optical windows, resulting in such problems that a wavelength conversion laser beam (that is, a light that has been wavelength-converted by the non-linear optical crystal) cannot be generated stably for a long period of time, and the vacuum vessel is required for a vessel and the device is expensive.
The present invention has been made in order to solve the above-mentioned problems, and therefore an object of the present invention is to provide a wavelength converting method and a wavelength converting device, and a wavelength conversion laser device and a laser machining device using the wavelength converting method and device which realize generating a light that has been wavelength-converted by the non-linear optical crystal stably for a long period of time.